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Chapter 6: 
Network Layer 
Introduction to Networks 
© 2008 Cisco Systems, Inc. All Presentation_ID rights reserved. Cisco...
Chapter 6: Objectives 
In this chapter, you will be able to: 
 Explain how network layer protocols and services support 
...
Chapter 6 
6.1 Network Layer Protocols 
6.2 Routing 
6.3 Routers 
6.4 Configuring a Cisco Router 
6.5 Summary 
Presentatio...
6.1 Network Layer Protocols 
© 2008 Cisco Systems, Inc. All Presentation_ID rights reserved. Cisco Confidential 4
Network Layer in Communication 
The Network Layer 
The network layer, or OSI Layer 3, provides services to allow end devic...
Network Layer in Communication 
Network Layer Protocols 
Common network layer protocols include: 
 IP version 4 (IPv4) 
...
IP Characteristics 
IP Components 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 7
Characteristics of the IP protocol 
IP - Connectionless 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. C...
Characteristics of the IP protocol 
Best Effort Delivery 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. ...
Characteristics of the IP protocol 
IP – Media Independent 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved...
IPv4 Packet 
Encapsulating IP 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 11
IPv4 Packet 
IPv4 Packet Header 
Contents of the IPv4 packet header 
Presentation_ID © 2008 Cisco Systems, Inc. All rights...
IPv4 Packet 
IPv4 Header Fields 
Contents of the IPv4 header fields 
Presentation_ID © 2008 Cisco Systems, Inc. All rights...
IPv4 Packet 
Sample IPv4 Headers 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 14
Network Layer in Communication 
Limitations of IPv4 
 IP Address depletion 
 Internet routing table expansion 
 Lack of...
Network Layer in Communication 
Introducing IPv6 
 Increased address space 
 Improved packet handling 
 Eliminates the ...
IPv6 Packet 
Encapsulating IPv6 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 17
IPv6 Packet 
IPv6 Packet Header 
Byte 1 Byte 2 Byte 3 Byte 4 
Version Traffic Class Flow Label 
Payload Length 
Next 
Head...
IPv6 Packet 
Sample IPv6 Header 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 19
6.2 Routing 
© 2008 Cisco Systems, Inc. All Presentation_ID rights reserved. Cisco Confidential 20
Host Routing Tables 
Host Packet Forwarding Decision 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisc...
Host Routing Tables 
Default Gateway 
Hosts must maintain their own, local, routing table to ensure that 
network layer pa...
Host Routing Tables 
IPv4 Host Routing Table 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confid...
Host Routing Tables 
Sample IPv4 Host Routing Table 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco...
Host Routing Tables 
Sample IPv6 Host Routing Table 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco...
Router Routing Tables 
Router Packet Forwarding Decision 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. ...
Router Routing Tables 
IPv4 Router Routing Table 
192.168.10.0/24 
R2 
192.168.11.0/24 
10.1.1.0/24 
10.1.2.0/24 
209.165....
Router Routing Tables 
Directly Connected Routing Table Entries 
192.168.10.0/24 
64.100.0.1 
R2 
192.168.11.0/24 
10.1.1....
Router Routing Tables 
Remote Network Routing Table Entries 
192.168.10.0/24 
64.100.0.1 
R2 
192.168.11.0/24 
10.1.1.0/24...
Router Routing Tables 
Next-Hop Address 
192.168.10.0/24 
64.100.0.1 
R2 
192.168.11.0/24 
10.1.1.0/24 
10.1.2.0/24 
209.1...
6.3 Routers 
© 2008 Cisco Systems, Inc. All Presentation_ID rights reserved. Cisco Confidential 31
Anatomy of a Router 
A Router is a Computer 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confide...
Anatomy of a Router 
Router CPU and OS 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential...
Anatomy of a Router 
Router Memory 
Memory 
Volatile / 
Non-Volatile 
Stores 
RAM Volatile 
• Running IOS 
• Running confi...
Anatomy of a Router 
Inside a Router 
1. Power 
Supply 
2. Shield for 
WIC 
3. Fan 
4. SDRAM 
5. NVRAM 
6. CPU 
7. Advance...
Anatomy of a Router 
Router Backplane 
Double-Wide EHWIC slots EHWIC 0 AUX 
Two 4 GB Flash Card Slots 
Port 
LAN 
Interfac...
Anatomy of a Router 
Connecting to a Router 
WAN 
Interface 
AUX 
Port 
LAN 
Interfaces 
Console 
RJ45 
Console 
USB Type ...
Anatomy of a Router 
LAN and WAN Interfaces 
Serial Interfaces 
LAN Interfaces 
Presentation_ID © 2008 Cisco Systems, Inc....
Router Boot-up 
Cisco IOS 
The Cisco IOS operational details vary on different internetworking devices, 
depending on the ...
Router Boot-up 
Bootset Files 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 40
Router Boot-up 
Router Bootup Process 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential ...
Router Boot-up 
Show Versions Output 
Router# show version 
Cisco IOS Software, C1900 Software (C1900-UNIVERSALK9-M), Vers...
6.4 Configuring a Cisco Router 
© 2008 Cisco Systems, Inc. All Presentation_ID rights reserved. Cisco Confidential 43
Configure Initial Settings 
Router Configuration Steps 
192.168.10.0/24 
192.168.11.0/24 
209.165.200.224 /30 
.10 
.10 
....
Configure Interfaces 
Configure LAN Interfaces 
192.168.10.0/24 
R2 
192.168.11.0/24 
10.1.1.0/24 
10.1.2.0/24 
209.165.20...
Configure Interfaces 
Verify Interface Configuration 
192.168.10.0/24 
R2 
192.168.11.0/24 
10.1.1.0/24 
10.1.2.0/24 
209....
Configuring the Default Gateway 
Default Gateway on a Host 
Default Gateway 
not needed 
192.168.10.0/24 
192.168.11.0/24 ...
Configuring the Default Gateway 
Default Gateway on a Switch 
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserv...
Network Layer 
Summary 
In this chapter, you learned: 
 The network layer, or OSI Layer 3, provides services to allow end...
Network Layer 
Summary (cont.) 
 In addition to hierarchical addressing, the network layer is also 
responsible for routi...
Network Layer 
Summary (cont.) 
 The routing table of a router stores information about directly-connected 
routes and re...
Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 52
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CCNA 1 Routing and Switching v5.0 Chapter 6

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CCNA 1 Routing and Switching v5.0 Chapter 6

  1. 1. Chapter 6: Network Layer Introduction to Networks © 2008 Cisco Systems, Inc. All Presentation_ID rights reserved. Cisco Confidential 1
  2. 2. Chapter 6: Objectives In this chapter, you will be able to:  Explain how network layer protocols and services support communications across data networks.  Explain how routers enable end-to-end connectivity in a small-to-medium- sized business network.  Determine the appropriate device to route traffic in a small-to-medium- sized business network.  Configure a router with basic configurations. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 2
  3. 3. Chapter 6 6.1 Network Layer Protocols 6.2 Routing 6.3 Routers 6.4 Configuring a Cisco Router 6.5 Summary Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 3
  4. 4. 6.1 Network Layer Protocols © 2008 Cisco Systems, Inc. All Presentation_ID rights reserved. Cisco Confidential 4
  5. 5. Network Layer in Communication The Network Layer The network layer, or OSI Layer 3, provides services to allow end devices to exchange data across the network. To accomplish this end-to-end transport, the network layer uses four basic processes:  Addressing end devices  Encapsulation  Routing  De-encapsulating Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 5
  6. 6. Network Layer in Communication Network Layer Protocols Common network layer protocols include:  IP version 4 (IPv4)  IP version 6 (IPv6) Legacy network layer protocols include:  Novell Internetwork Packet Exchange (IPX)  AppleTalk  Connectionless Network Service (CLNS/DECNet) Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 6
  7. 7. IP Characteristics IP Components Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 7
  8. 8. Characteristics of the IP protocol IP - Connectionless Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 8
  9. 9. Characteristics of the IP protocol Best Effort Delivery Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 9
  10. 10. Characteristics of the IP protocol IP – Media Independent Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 10
  11. 11. IPv4 Packet Encapsulating IP Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 11
  12. 12. IPv4 Packet IPv4 Packet Header Contents of the IPv4 packet header Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 12
  13. 13. IPv4 Packet IPv4 Header Fields Contents of the IPv4 header fields Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 13
  14. 14. IPv4 Packet Sample IPv4 Headers Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 14
  15. 15. Network Layer in Communication Limitations of IPv4  IP Address depletion  Internet routing table expansion  Lack of end-to-end connectivity Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 15
  16. 16. Network Layer in Communication Introducing IPv6  Increased address space  Improved packet handling  Eliminates the need for NAT  Integrated security  4 billion IPv4 addresses 4,000,000,000  340 undecillion IPv6 addresses 340,000,000,000,000,000,000,000,000,000,000,000,000 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 16
  17. 17. IPv6 Packet Encapsulating IPv6 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 17
  18. 18. IPv6 Packet IPv6 Packet Header Byte 1 Byte 2 Byte 3 Byte 4 Version Traffic Class Flow Label Payload Length Next Header Hop Limit Source IP Address Destination IP Address Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 18
  19. 19. IPv6 Packet Sample IPv6 Header Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 19
  20. 20. 6.2 Routing © 2008 Cisco Systems, Inc. All Presentation_ID rights reserved. Cisco Confidential 20
  21. 21. Host Routing Tables Host Packet Forwarding Decision Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 21
  22. 22. Host Routing Tables Default Gateway Hosts must maintain their own, local, routing table to ensure that network layer packets are directed to the correct destination network. The local table of the host typically contains:  Direct connection  Local network route  Local default route R Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 22
  23. 23. Host Routing Tables IPv4 Host Routing Table Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 23
  24. 24. Host Routing Tables Sample IPv4 Host Routing Table Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 24
  25. 25. Host Routing Tables Sample IPv6 Host Routing Table Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 25
  26. 26. Router Routing Tables Router Packet Forwarding Decision Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 26
  27. 27. Router Routing Tables IPv4 Router Routing Table 192.168.10.0/24 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30 .226 .10 .10 .1 .225 S0/0/0 G0/0 .1 R1 .1 .1 G0/1 R1#show ip route Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks D 10.1.1.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 D 10.1.2.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 192.168.10.0/24 is variably subnetted, 2 subnets, 3 masks C 192.168.10.0/24 is directly connected, GigabitEthernet0/0 L 192.168.10.1/32 is directly connected, GigabitEthernet0/0 192.168.11.0/24 is variably subnetted, 2 subnets, 3 masks C 192.168.11.0/24 is directly connected, GigabitEthernet0/1 L 192.168.11.1/32 is directly connected, GigabitEthernet0/1 209.165.200.0/24 is variably subnetted, 2 subnets, 3 masks C 209.165.200.224/30 is directly connected, Serial0/0/0 L 209.165.200.225/32 is directly connected, Serial0/0/0 R1# .10 .10 PC1 PC2 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 27
  28. 28. Router Routing Tables Directly Connected Routing Table Entries 192.168.10.0/24 64.100.0.1 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30 .226 .10 .10 .1 .1 G0/0 .1 .1 G0/1 .225 S0/0/0 R1 A B C .10 .10 C 192.168.10.0/24 is directly connected, GigabitEthernet0/0 L 192.168.10.1/32 is directly connected, GigabitEthernet0/0 A Identifies how the network was learned by the router. B Identifies the destination network and how it is connected. C Identifies the interface on the router connected to the destination network. PC1 PC2 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 28
  29. 29. Router Routing Tables Remote Network Routing Table Entries 192.168.10.0/24 64.100.0.1 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30 .226 .10 .10 .10 .10 .1 .1 G0/0 .1 .1 G0/1 .225 S0/0/0 R1 PC1 PC2 D 10.1.1.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 A Identifies how the network was learned by the router. B Identifies the destination network. C Identifies the administrative distance (trustworthiness) of the route source. D Identifies the metric to reach the remote network. E Identifies the next hop IP address to reach the remote network. F Identifies the amount of elapsed time since the network was discovered. G Identifies the outgoing interface on the router to reach the destination network. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 29
  30. 30. Router Routing Tables Next-Hop Address 192.168.10.0/24 64.100.0.1 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30 .226 .10 .10 .10 .10 .1 .1 G0/0 .1 .1 G0/1 .225 S0/0/0 R1 PC1 PC2 R1#show ip route Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks D 10.1.1.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 D 10.1.2.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 192.168.10.0/24 is variably subnetted, 2 subnets, 3 masks C 192.168.10.0/24 is directly connected, GigabitEthernet0/0 L 192.168.10.1/32 is directly connected, GigabitEthernet0/0 192.168.11.0/24 is variably subnetted, 2 subnets, 3 masks C 192.168.11.0/24 is directly connected, GigabitEthernet0/1 L 192.168.11.1/32 is directly connected, GigabitEthernet0/1 209.165.200.0/24 is variably subnetted, 2 subnets, 3 masks C 209.165.200.224/30 is directly connected, Serial0/0/0 L 209.165.200.225/32 is directly connected, Serial0/0/0 R1# Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 30
  31. 31. 6.3 Routers © 2008 Cisco Systems, Inc. All Presentation_ID rights reserved. Cisco Confidential 31
  32. 32. Anatomy of a Router A Router is a Computer Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 32
  33. 33. Anatomy of a Router Router CPU and OS Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 33
  34. 34. Anatomy of a Router Router Memory Memory Volatile / Non-Volatile Stores RAM Volatile • Running IOS • Running configuration file • IP routing and ARP tables • Packet buffer ROM Non-Volatile • Bootup instructions • Basic diagnostic software • Limited IOS NVRAM Non-Volatile • Startup configuration file Flash Non-Volatile • IOS • Other system files Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 34
  35. 35. Anatomy of a Router Inside a Router 1. Power Supply 2. Shield for WIC 3. Fan 4. SDRAM 5. NVRAM 6. CPU 7. Advanced Integration Module (AIM) 1 2 2 6 5 3 4 7 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 35
  36. 36. Anatomy of a Router Router Backplane Double-Wide EHWIC slots EHWIC 0 AUX Two 4 GB Flash Card Slots Port LAN Interfaces USB Ports Console RJ45 Console USB Type B Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 36
  37. 37. Anatomy of a Router Connecting to a Router WAN Interface AUX Port LAN Interfaces Console RJ45 Console USB Type B Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 37
  38. 38. Anatomy of a Router LAN and WAN Interfaces Serial Interfaces LAN Interfaces Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 38
  39. 39. Router Boot-up Cisco IOS The Cisco IOS operational details vary on different internetworking devices, depending on the device’s purpose and feature set. However, Cisco IOS for routers provides the following:  Addressing  Interfaces  Routing  Security  QoS  Resources Management Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 39
  40. 40. Router Boot-up Bootset Files Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 40
  41. 41. Router Boot-up Router Bootup Process Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 41
  42. 42. Router Boot-up Show Versions Output Router# show version Cisco IOS Software, C1900 Software (C1900-UNIVERSALK9-M), Version 15.2(4)M1, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2012 by Cisco Systems, Inc. Compiled Thu 26-Jul-12 19:34 by prod_rel_team ROM: System Bootstrap, Version 15.0(1r)M15, RELEASE SOFTWARE (fc1) Router uptime is 10 hours, 9 minutes System returned to ROM by power-on System image file is "flash0:c1900-universalk9-mz.SPA.152-4.M1.bin" Last reload type: Normal Reload Last reload reason: power-on <Output omitted> Cisco CISCO1941/K9 (revision 1.0) with 446464K/77824K bytes of memory. Processor board ID FTX1636848Z 2 Gigabit Ethernet interfaces 2 Serial(sync/async) interfaces 1 terminal line DRAM configuration is 64 bits wide with parity disabled. 255K bytes of non-volatile configuration memory. 250880K bytes of ATA System CompactFlash 0 (Read/Write) <Output omitted> Technology Package License Information for Module:'c1900' ----------------------------------------------------------------- Technology Technology-package Technology-package Current Type Next reboot ------------------------------------------------------------------ ipbase ipbasek9 Permanent ipbasek9 security None None None data None None None Configuration register is 0x2142 (will be 0x2102 at next reload) Router# Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 42
  43. 43. 6.4 Configuring a Cisco Router © 2008 Cisco Systems, Inc. All Presentation_ID rights reserved. Cisco Confidential 43
  44. 44. Configure Initial Settings Router Configuration Steps 192.168.10.0/24 192.168.11.0/24 209.165.200.224 /30 .10 .10 .225 S0/0/0 G0/0 .1 R1 .1 .1 G0/1 PC1 PC2 Router> enable Router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)# hostname R1 R1(config)# R2 10.1.1.0/24 10.1.2.0/24 .226 .10 .10 .1 Router> en Router# conf t Enter configuration commands, one per line. End with CNTL/Z. Router(config)# ho R1 R2(config)# OR R1(config)# enable secret class R1(config)# R1(config)# line console 0 R1(config-line)# password cisco R1(config-line)# login R1(config-line)# exit R1(config)# R1(config)# line vty 0 4 R1(config-line)# password cisco R1(config-line)# login R1(config-line)# exit R1(config)# R1(config)# service password-encryption R1(config)# R1(config)# banner motd # Enter TEXT message. End with the character '#'. *********************************************** WARNING: Unauthorized access is prohibited! *********************************************** # R1(config)# R1# copy running-config startup-config Destination filename [startup-config]? Building configuration... [OK] R1# Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 44
  45. 45. Configure Interfaces Configure LAN Interfaces 192.168.10.0/24 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30 .226 .10 .10 .10 .10 .1 .225 S0/0/0 G0/0 .1 R1 .1 .1 G0/1 PC1 PC2 R1# conf t Enter configuration commands, one per line. End with CNTL/Z. R1(config)# R1(config)# interface gigabitethernet 0/0 R1(config-if)# ip address 192.168.10.1 255.255.255.0 R1(config-if)# description Link to LAN-10 R1(config-if)# no shutdown %LINK-5-CHANGED: Interface GigabitEthernet0/0, changed state to up %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to up R1(config-if)# exit R1(config)# R1(config)# int g0/1 R1(config-if)# ip add 192.168.11.1 255.255.255.0 R1(config-if)# des Link to LAN-11 R1(config-if)# no shut %LINK-5-CHANGED: Interface GigabitEthernet0/1, changed state to up %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to up R1(config-if)# exit R1(config)# Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 45
  46. 46. Configure Interfaces Verify Interface Configuration 192.168.10.0/24 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30 .226 .10 .10 .10 .10 .1 .225 S0/0/0 G0/0 .1 R1 .1 .1 G0/1 PC1 PC2 R1# show ip interface brief Interface IP-Address OK? Method Status Protocol GigabitEthernet0/0 192.168.10.1 YES manual up up GigabitEthernet0/1 192.168.11.1 YES manual up up Serial0/0/0 209.165.200.225 YES manual up up Serial0/0/1 unassigned YES NVRAM administratively down down Vlan1 unassigned YES NVRAM administratively down down R1# R1# ping 209.165.200.226 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 209.165.200.226, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/9 ms R1# Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 46
  47. 47. Configuring the Default Gateway Default Gateway on a Host Default Gateway not needed 192.168.10.0/24 192.168.11.0/24 .1 G0/0 R1 G0/1 .1 .10 PC1 .10 PC2 .10 .10 PC3 PC4 Default Gateway needed 192.168.10.0/24 192.168.11.0/24 .1 G0/0 R1 G0/1 .1 .10 PC1 .11 PC2 .10 .11 PC3 PC4 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 47
  48. 48. Configuring the Default Gateway Default Gateway on a Switch Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 48
  49. 49. Network Layer Summary In this chapter, you learned:  The network layer, or OSI Layer 3, provides services to allow end devices to exchange data across the network.  The network layer uses four basic processes: IP addressing for end devices, encapsulation, routing, and de-encapsulation.  The Internet is largely based on IPv4, which is still the most widely-used network layer protocol.  An IPv4 packet contains the IP header and the payload.  The IPv6 simplified header offers several advantages over IPv4, including better routing efficiency, simplified extension headers, and capability for per-flow processing. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 49
  50. 50. Network Layer Summary (cont.)  In addition to hierarchical addressing, the network layer is also responsible for routing.  Hosts require a local routing table to ensure that packets are directed to the correct destination network.  The local default route is the route to the default gateway.  The default gateway is the IP address of a router interface connected to the local network.  When a router, such as the default gateway, receives a packet, it examines the destination IP address to determine the destination network. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 50
  51. 51. Network Layer Summary (cont.)  The routing table of a router stores information about directly-connected routes and remote routes to IP networks. If the router has an entry in its routing table for the destination network, the router forwards the packet. If no routing entry exists, the router may forward the packet to its own default route, if one is configured or it will drop the packet.  Routing table entries can be configured manually on each router to provide static routing or the routers may communicate route information dynamically between each other using a routing protocol.  For routers to be reachable, the router interface must be configured. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 51
  52. 52. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 52

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